Scanning tunneling microscopy and spectroscopy studies of the surface structure and electronic properties of single-crystal Tl–Ba–Ca–Cu–O superconductors

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) have been used to characterize the surface structure and electronic properties of Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10 single crystals. Atomic resolution STM images show that 90%–95% of the surface has a near-trigonal structure with a=b=0.24 nm and an a–b angle of 65°. The remaining 5%–10% of the surface consists of a new orthorhombic structure with a=b=0.40 nm. Spatially resolved STS measurements further demonstrate that regions with the 0.24 nm period structure are metallic, while areas with the 0.40 nm period structure are semiconducting.